The present invention relates to a magnetic card having a plurality of stacked magnetic layers on which information is recorded in distribution, and a magnetic shielding layer which is located uppermost and used for shielding information.
In the prior art, a magnetic card of the multi-layer structure type is well known, as disclosed in Japanese Patent Disclosure (Kokai) No. 51-129209. FIG. 1 shows a magnetic card of this type. As shown, substrate 1 is overlaid with first magnetic layer 2, which is in turn overlaid with non-magnetic intermediate layer 30. Second magnetic layer 4 is laid over non-magnetic intermediate layer 30, and protection layer 50 is provided as an uppermost layer such that it covers the upper side of second magnetic layer 4. This laminated structure is employed so as to prevent the magnetic card from being forged or to prevent the information recorded on the card from being altered. Authentic data is recorded on first magnetic layer 2, while counterfeit data is recorded on second magnetic layer 4. Non-magnetic intermediate layer 30 is formed of .alpha.-Fe.sub.2 O.sub.3, for example. Uppermost protection layer 50 is formed of a synthetic resin, for example.
It is recently found, however, that the counterfeit data recorded in second magnetic layer 4 can be easily erased by means of a so-called "paper clip magnet" or the like. If the counterfeit data is erased, the authentic data recorded on first magnetic layer 2 can be easily reproduced for decoding, by use of an ordinary technique. Therefore, it has become difficult to prevent the magnetic card from being fraudulently used by an unauthorized person or to prevent the information on the card from being forged or altered.
Furthermore, the thickness of non-magnetic intermediate layer 30 causes a spacing loss at the time of reproducing data from first magnetic layer 2. Therefore, the data is not always read out accurately from first magnetic layer 2.